The present invention relates to a vehicle brake system comprising a hydraulically controllable disk brake device, which has an electromechanical actuating device for activating a parking brake function, wherein the vehicle brake system has a hydraulic circuit having a hydraulic pressure source and controllable functional elements in order to hydraulically control the disk brake device according to a service brake action of a driver or according to an automatic activation of a driving assistance system, wherein the vehicle brake system further comprises a control device in order to control the electromechanical actuating device according to a parking brake action of the driver or according to an automatic activation of the parking brake function. The invention further relates to a method for controlling a vehicle brake system of the previously described type.
A variety of vehicle brake systems are known from the background art. Specifically the document DE 10 2005 051 082 A1, and corresponding U.S. Pat. No. 8,322,495 B2, both of which are incorporated by reference herein in entirety, describes a vehicle brake system having a disk brake that is designed as a floating caliper disk brake. In this case, a friction lining arrangement comprising two opposing friction linings on either side of a brake disk is provided. The one brake lining is attached to a floating caliper, while the other brake lining may be hydraulically displaced relative to the floating caliper by means of an actuating piston. As a result of a hydraulic loading of an actuating piston the movable brake lining is displaced towards the brake disk. The brake lining fixed to the floating caliper is in an, as such, known manner pulled towards the brake disk from the other side by means of the floating caliper function, so that a braking force acts from both sides upon the brake disk.
In addition to this floating caliper function, which has been known for a long time, this background art moreover also provides an electromechanical actuating device. This is used to realize a parking brake function. Given corresponding control the disk brake, besides the hydraulic displacement, may in addition be actuated electromechanically. To avoid having to dimension the electromechanical components, in particular the electric motor, far too large and powerful, it may be provided that the activation of the parking brake is assisted hydraulically. In other words the brake is hydraulically preloaded, the hydraulic preloading pressure is maintained and the parking brake is then blocked by means of the electromechanical actuating device. In a correspondingly elaborate manner hydraulic assistance also has to be provided for releasing the parking brake function.
From the prior art WO 2005/073043 A1, and corresponding U.S. Pat. No. 7,744,166 B2, both of which are incorporated by reference herein in entirety, a corresponding disk brake device and a method of controlling this disk brake device are further known, whereby using various sensors and employing predetermined mathematical models in dependence upon the actual operating situation, such as for example a loaded state of the vehicle or an inclination of the road, it is possible also to generate braking forces that lie substantially above the braking forces that may be generated solely by the electromechanical actuating device.
It has however emerged that, given such a combination of hydraulic and electromechanical brake, because of the high collective load of hydraulically and electromechanically generated brake application forces upon activation of the parking brake function the electromechanical components of the electromechanical actuating device have to be designed with a corresponding load rating in order to avoid failure. Particularly during the subsequent release of the parking brake it is then namely necessary to overcome the brake application force, which is generated hydraulically and mechanically in order to activate the parking brake function and is, as it were, conserved during the braking state, by means of a correspondingly powerful mechanism or using hydraulic assistance.